Demethylation of methoxy groups

Another important use of BCl is as a Ftiedel-Crafts catalyst ia various polymerisation, alkylation, and acylation reactions, and ia other organic syntheses (see Friedel-Crafts reaction). Examples include conversion of cyclophosphasenes to polymers (81,82) polymerisation of olefins such as ethylene (75,83—88) graft polymerisation of vinyl chloride and isobutylene (89) stereospecific polymerisation of propylene (90) copolymerisation of isobutylene and styrene (91,92), and other unsaturated aromatics with maleic anhydride (93) polymerisation of norhornene (94), butadiene (95) preparation of electrically conducting epoxy resins (96), and polymers containing B and N (97) and selective demethylation of methoxy groups ortho to OH groups (98). 

Decarbonylation of 2-[ F]fluorobenzaldehydes has been used to synthesize labeled arenes with nonactivated substituents, e.g., 4-bromo-[ F]fiuorobenzene from 3-bromo-6-nitrobenzaldehyde (Chakraborty and Kilbourn 1991a). This methodology was also applied to [ Fjfluoroarylketones (Allain-Barbier et al. 1998 Forngren et al. 1998) and to mono- to tetra-methoxy-substituted [ F]fluorobenzenes from the corresponding 2-nitro(methoxy) benzaldehydes (Shen et al. 2009). In the latter study they identified side products, which derived from demethylation of methoxy groups and intramolecular redox processes that reduced the radiochemical yields. 

This ring is foimed by reaction between a side-chain nitriie and a phenolic group the latter is produced in situ by demethyiation of an ether with pyridine hydrochloride which also acts as a cyclizing agent and demethylates another methoxy group. 

Thebaine (192) is found in numerous plants of the sections Orthorhoeades, Pilosa, Miltantha, and Macrantha. The phenolic ortho-para oxidation leading to the formation of thebaine is shown to be a common phenomenon, whereas the specific ability to demethylate the methoxy groups to produce morphine (204) or codeine (198) appears to be a rare characteristic (Fig. 4). 

Demethylation of trequinsin (3) with a 65 35 mixture of AcOH and 48% HBr at 115 °C for 3 h gave mainly 10-hydroxyl derivatives 148 (R = r = H), which was accompanied by traces of its 9-hydroxyl and 9,10-dihydroxy derivatives. In boiling 48% HBr for 2 h its 9,10-dihydroxy derivative formed in 63% yield (98IJC(B)1). 9-Methoxy group of 3 and that of its 2-[(2,6-dimethyl-4-carboxyphenyl)imino] derivative 178 (R = COOH) was selectively demethylated by the treatment with 60% NaOH and EtSH in HMPA. Treatment of 3 with pyridine HCl in boiling pyridine for 20 min afforded its 9,10-dihydroxy-3-desmethyl derivative in 65% yield. 4 -Hydroxymethyl... 

Condensation of adipic acid derivative 17 with phenylethylamine in the presence of carbo-nyldiimidazole affords the bis-adipic acid amide 18. The synthesis is completed by reduction of the carbonyl groups with diborane followed by demethylation of the aromatic methoxy groups with hydrogen bromide the afford dopexamine (19) [3]. 

Many of the premetallised direct dyes are symmetrical structures in the form of bis-1 1 complexes with two copper(II) ions per disazo dye molecule. Scheme 5.12 illustrates conversion of the important unmetallised royal blue Cl Direct Blue 15 (5.43), derived from tetrazotised dianisidine coupled with two moles of H acid, to its much greener copper-complex Blue 218 (5.44) with demethylation of the methoxy groups as described above. Important symmetrical red disazo structures of high light fastness, such as Cl Direct Red 83 (5.45), contain two J acid residues linked via their imino groups. Unsymmetrical disazo blues derived from dianisidine often contain a J acid residue as one ligand and a different coupler as the other, such as Oxy Koch acid in Cl Direct Blue 77 (5.46), for example. 

Demethylation of the methoxy groups in lactone 142 was achieved with BBr3 in dichloromethane. The reaction conditions were not optimized, and the yield of a-hydroxylated enterolactone 144 was low (15%). Several byproducts, such as both regioisomers of the mono-methylether, were obtained. 

Metabolism of maduramicin in various animal species seems to proceed in a manner similar to monensin. Selective 0-demethylation of one or two methoxy groups has been reported as the major biotransformation route in chickens and rats (30), whereas O-demethylation of one or more methoxy groups followed by hydroxylation is the major biotransformation route in turkey excreta (31). Conjugation with glucuronic acid also occurs but it is of minor metabolic importance. 

Residues in liver of poultry sacrificed at 6 h after withdrawal, were comprised of unchanged semduramicin at a percentage of 45%, whereas an array of more polar, low-level ( 0.1 ppm) metabolites could be also detected. Using bile as a source of major semduramicin metabolites, the metabolism of semduramicin was spectrometrically determined to proceed by (9-demethylation of the methoxy groups in the A and G rings, as it has been also described for maduramicin (30, 31) and monensin (21, 44). 

ZEISEL REACTION. The demethylation of an organic compound by treatment with hydriodic acid, which leaves a hydroxy group in place of the methoxy group, and forms methyl iodide, which may readily be determined quantitatively, as in the study of the amount of methoxy gioups present. 

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